1. Field of the Invention
The invention relates to a multiple-injection molding apparatus, and more particularly, to an apparatus that provides multiple injection capability by using a plurality of separate single-injection unit molding machines.
Computer keyboard keys and telephone touchtone keys are among the plastic items that are produced utilizing a multiple-injection molding process. The alphanumeric characters on the face of such keys are formed from a first plastic which extends through a second plastic forming the body of the keys. Such keys are usually created in a two-step process. In the first step, the alphanumeric character is molded as a raised protrusion on a body which in the finished key forms an inner layer of the key. In a second step, a second plastic is molded around the body formed in the first step, the depth of the second plastic matching the height that the alphanumeric character is raised from that body. In a finished key the top of the alphanumeric character extends flush with the surface of the second plastic. Though someone using such keys may have the illusion that the characters are only surface deep, those characters last as long as the keys.
2. Description of the Related Art
There are several methods of creating keys with alphanumeric characters using double-injection molding. One of the methods uses the `swing plate mold` disclosed in U.S. Pat. No. 5,020,215, granted on Jun. 4, 1991 and entitled `Method Of An Apparatus for Manufacturing A Keyboard`. In this method, the mold assembly includes a stationery upper-half mold, a movable and rotatable lower-half mold, and a movable support plate fastened to the bottom of the lower-half mold. The lower-half mold is mounted on an axle capable of rotating it between two positions 180.degree. apart. The cores of the mold assembly are bolted to the support plate and during the injection process extend through the lower-half mold into corresponding cavities in the upper-half mold. A first set of cores and cavities are configured to create an inner plastic body for each of the keys, those inner bodies having the alphanumeric characters as protrusions; a second set of cores and cavities are configured to create the outer plastic body of each key. At a first angular orientation, the lower-half mold is pressed between the upper-half mold and the support plate. In a first injection molding step, the first set of cores and cavities are used to create a set of the inner plastic bodies on one side of the lower-half mold. The upper-half mold and the support plate are then separated from the lower-half mold that holds the inner plastic bodies, and the lower-half mold is rotated 180.degree.. The lower-half mold is then again pressed between the upper-half mold and the support plate, and in a second injection molding step the second set of cores and cavities are used to create the outer plastic body of each key. A removal arm on the mold assembly removes the keys from the lower-half mold by suction after the two-step injection molding.
There are certain disadvantages to the `swing plate mold` apparatus described above. Firstly, this type of apparatus requires a double injection unit capability in the same machine, which increases both cost and complexity. Secondly, the mold platens must be large enough to accommodate the required number of molded items for both injection steps.